1. Field of the Invention
The invention relates generally to an electroluminescent device (hereinafter, xe2x80x9cELDxe2x80x9d) and method of manufacturing the same. More particularly, it relates to an electroluminescent device and method of manufacturing the same, capable of reducing the loss of light propagated along the lateral side of the device and increasing the amount of light propagated to the front of the display to improve the brightness and efficiency of the device, in such a way that a transparent conductive film or a luminescent layer is made of materials having crystallographic anisotropy and is then etched to make the transparent conductive film or the luminescent layer with a protrusion shaped or textured surface feature.
2. Description of the Prior Art
An electroluminescence device (hereinafter, xe2x80x9cELDxe2x80x9d) is one using an electroluminescent phenomena occurring when an electric field is applied to materials such as ZnS, CaS, and the like. SHARP (Japan) announced a thin ELD having a high brightness and a long life (1974). Since then, many researches have been made on the ELD. In particular, C. W. Tang in Eastman Kodak manufactured a thin film ELD using an organic material and reported that a green luminescence of high brightness is possible. As the result, researches have been actively made on an organic ELD having a low driving voltage and being advantageous in the process.
The structure of the ELD may mainly includes an alternating-current thin film type structure, an alternating-current thick film type structure, a direct-current thin film type structure and a direct-current thick film type structure. In detail, the structure of the alternating-current thin film type structure usually includes upper and lower insulating layers with a luminescent layer intervened between them, and the alternating-current thick film type structure including an luminescent material mixed with insulating binder and an insulating layer. Also, the structure of the direct-current type structure includes a thin film type structure having a single insulating layer and a luminescent layer, and a thick film type structure having a luminescent layer.
A structure of a conventional ELD 10 will be described by reference to FIG. 1.
As shown in FIG. 1, the alternating-current thin film ELD 10 includes a transparent substrate such as glass 11, or semiconductor single crystal substrates such as silicon 11 or a flexible substrate 11. A lower electrode 12 as a transparent electrode is formed on the substrate 11. A lower insulating layer 13 formed on the lower electrode 12. A luminescent layer 14 is formed on the lower insulating layer 13. An upper insulating layer 15 is formed on the luminescent layer 14. An upper electrode 16 made of a transparent electrode or a metal electrode is formed on the upper insulating layer 15.
FIG. 10 and FIG. 11 show schematic diagram of the crystal structure and the surface atom arrangement for II-VI and III-V compounds, respectively. III-V group compounds have a cubic or hexagonal structure. In FIG. 10, A/Axe2x80x2 indicate II group or III group atoms and B/Bxe2x80x2 indicate VI group or V group atoms. Also, the direction of the arrows is (111) in case of the cubic system and (0001) in case of the hexagonal system. Also, FIG. 11 shows the electron arrangement of A and B atoms each constituting {0001} or {111} crystal surfaces of II-VI group or III-V group compound. In FIG. 11, A indicates II group or III group atoms and B indicates VI group or V group atoms.
However, the conventional ELD 10 having this structure did not have the brightness and efficiency sufficient to be applicable to the display requiring a high brightness and efficiency. Therefore, there is an urgent need for a new ELD having a high brightness and efficiency.
In order to solve this problem, many researches haven been made on a new ELD having these high brightness and efficiency characteristics. For example, the crystallinity of phosphor materials constituting the ELD, the degree of activation for activator ions, the number of accelerated electrons, and the energy and its distribution must be controlled. For this, a method of manufacturing various phosphor materials and an annealing method for the purpose of an improved crystal property of the phosphor materials and an effective activation of the activator ions. Also, there has been proposed a method of using an insulating material having high dielectric constant in order to generate accelerated electrons having high energy of narrow energy distribution.
Meanwhile, in order to manufacture a ELD of a high brightness and a high efficiency as described above, a solution by which the amount of light emitted toward the lateral side of the ELD display is promising. As the surface and flatness of the film adopted in the conventional ELD is usually smooth and good, 80xcx9c90% of emitted lights from activator ions actually propagate along the interface between the insulating layer and the luminescent layer or the interface between the insulating layer and the electrode layer and can not emitted to front side due to so called xe2x80x9cLight-Pipingxe2x80x9d or xe2x80x9cWaveguidexe2x80x9d effect. Due to this, the light traveling toward the front of the display that can contribute an actual optical efficiency is only 10xcx9c20% of the total.
The present invention is contrived to solve the above problems and an object of the present invention is to increase the scattering of light by deforming the surface of a film constituting an ELD in order to manufacture the ELD having a high brightness and high efficiency.
Further, another object of the present invention is to simplify the process by applying ZnO that can be relatively easily etched as compared to the transparent electrode made of conventional indium tin oxide (hereinafter, xe2x80x9cITOxe2x80x9d) to a process of forming the transparent electrode.
In order to accomplish the above object, an electroluminescent device according to the present invention is characterized in that it comprises a substrate, a first electrode formed on the substrate, a luminescent layer formed on the first electrode, and a second electrode formed on the luminescent layer, wherein at least one of the first electrode, the luminescent layer and the second electrode is formed to have a protrusion or texture at its surface.
Preferably, the electroluminescent device further includes a first insulating layer formed between the first electrode and the luminescent layer; and a second insulating layer formed between the luminescent layer and the second electrode.